The general aim of this project is to elucidate mechanisms by which proteins and viruses enter cells by receptor-mediated transport processes and translocate across the lipid bilayer to cytosol and nuclear compartments. Molecular signals which lead to unique vesicle trafficking are studied. Basic knowledge from these processes is used to design targeted drug delivery systems such as immunotoxins. Anti-human CD3 immunotoxins constructed with CRM9, a binding site mutant of diphtheria toxin, eliminate 80% of established tumors of human T cell leukemia in a nude mouse xenograft system. The cell killing power of the immunotoxin, when delivered at 1/2 the guinea pig minimum lethal dose, is equivalent to 500-600 cGy from a 137Cs source and produces a 3 log kill of tumor cells. The therapeutic margin appears promising for clinical application which might include treatments for AIDS, autoimmune diseases and graft-versus-host-disease following bone marrow transplantation. The relationship between target cell number and immunotoxin-mediated in vivo cell depletion have been characterized. Target cell log kill was found to be inversely proportional to cell number at constant immunotoxin levels. The mathematical relationship permits an estimate of required conjugate to achieve a desired log kill. Early and late steps in basal-lateral routing of vesicular stomatitis virus are dependent upon electrical potential in epithelial (MDCK) cells: Apical routing is potential independent. Thus in this polarized epithelium the basal-later membrane contains an additional constraint which can be varied by the basal-lateral K+ current.